1. Beat butter with an electric mixer on medium to high speed 30 seconds or until softened. Add sugar and baking powder. Beat until combined. Beat in whole egg, egg yolk, and vanilla until well combined. Using a wooden spoon, stir in flour and cocoa powder. Divide dough in half. Cover and chill dough 1 hour or until easy to handle.

2. On a lightly floured surface, roll each portion of dough to 1/8- inch thickness. Using a 2- 1/2 cup cookie cutter dipped in flour, cut dough into rounds. Place half of the rounds 1- inch apart on an ungreased cookie sheet. Spoon a rounded teaspoon of Fudge Filling into the center of each round. Place another round over top of filling. Press edges together to seal. Bake ina 350 degrees F oven 10 to 12 minutes or until edges are firm. Cool on cookie sheet 1 minute. Remove from cookie sheet and cool on a wire rack. Place in an airtight container and chill for up to 2 days.

Fudge Filling: In a heavy small saucepan melt 4 ounces semisweet chocolate over low heat, stirring constantly. Remove from heat. Stir in 1/2 cup dairy sour cream and 1/4 cup finely chopped walnuts. Mixture will stiffen as it cools.